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Adjustment of polygonal covers

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Digitization often goes beyond simple object tracing and attributive data input; it comprises forming of an integrate and topologically correct polygonal cover. Easy Trace Pro has several useful tools and utilities for this purpose.

To adjust two polygonal covers, you should select one of them as more reliable and fit the second cover to it.

Let us consider an ordinary situation – a polygon of wood crossed by a polygon of road. We digitize the road center line, generate a band polygon around it, and subtract the road from the wood.

Everything becomes problematic if the road is already cut out. The operation could generate objectionable slits (holes) in the polygonal cover. In that case, act as follows:
  1. If the slits are small and your Easy Trace version is 8.5 or better, just run the Topology Correction utility. Specify the “Road” layer as a reference one and correct objects from the “Wood” layer applying the “Adjust polyline segments within given radius” operation.

  2. If the version is older and the slits are rather wide, manual correction becomes unavoidable. Run the Check Polygons utility with the “Search for holes” option. Detected polygons of slits will be attributed to the _ERRORS_ layer. Then you select the polygon of wood with the Editor, start joining mode (E), and click all these polygons to add them to the wood. It is better to freeze the “Road” layer beforehand as it is quite possible to click it by mistake

  3. We recommend running of Topology Correction before the check even if the utility can not adjust polygon boundaries in your ET version. The most narrow and troublesome slits may be repaired by the "Contract vertices within given radius" operation.

Now, let us consider the method of road subtraction from the wood:

Apply the Polygon Subtraction utility if your Easy Trace version is 8.6 or better.

For older versions, apply the Shears tool in the following way:

  1. First of all, switch off all irrelevant layers and freeze the “cutting” layer otherwise it may dissect its own objects.

    Or you may select the layer - “victim” explicitly from the list in the Parameters Bar of the Shears tool.

  2. Then form the cutting contour and press Alt+W.

    If you are lucky, the contour already exists and you just select it with the Group Editor; if not – hold Ctrl pressed and select contours. It may be reasonable to do it in several movements. To facilitate control, make “cutting” polygons transparent and use filling for the underlying polygonal layer – then you will easily see where polygon subtraction is already executed.

    Make a copy of the project folder (including DB subfolder) before you cut out anything – something may go wrong at the first attempt!

Note

If the process takes too much time...

Your ET version is rather old. Our former algorithm was a typical quadratic one – it compared every cutting polygon with every “victim”. Correspondingly, the process will be four times faster if you halve the number of cutting polygons, etc. So, the only way out is to attribute cutting polygons to different layers

How to adjust linear and polygonal covers?

A road or a river may serve as a boundary of a forestland for example. If the wood polygon was generated applying these lines, it does not require any adjustment. But suppose that lines and polygons were digitized independently. If that is the case, act as follows:

  1. Topology Correction with forming of common vertices at crossings of polylines and polygon boundaries (beginning from Version 8.5, you may specify layers of linear objects as reference ones and additionally adjust polygon boundaries).
  2. Take the Curvilinear Tracer, make the “Wood” layer current, and press «H» hot key to start the Quick polygon creation mode.
  3. Click inside slits in the polygonal cover with the cursor (“hand”) to generate polygons – plugs for these slits. Then you select the polygon of wood with the Editor, start joining mode (E), and click all these polygons to add them to the wood.
  4. Press Shift to start the «Cut off and delete the polygon part» mode. The cursor-«hand» becomes red, and one touch is sufficient now to delete all parts of the wood polygon protruded beyond the line of the road.
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